1. Field of the Invention
This invention relates to the field of reinforced glass structures in general, and in particular, to laminated safety glass reinforced with ionomer resin films and/or polycarbonates. Laminates of glass, ionomer resin, and metal are also contemplated in the invention.
2. Description of Prior Art
Safety glass can be reinforced by lamination with an inner layer of polycarbonate. The resulting lamination, however, is impractical for two principal reasons. One reason is insufficient bond strength when the polycarbonate is bonded directly to the glass. A second, and even more important reason stems from polycarbonate and glass having different co-efficients of thermal expansion. Safety glass laminates made by bonding polycarbonate directly to glass will delaminate on cooling from the temperature necessary to bond glass and polycarbonate, due to the different thermal expansion co-efficients of the components.
Initial attempts to solve these problems involved interposing additional interlayers of polyvinyl butyral (PVB) between the polycarbonate and the glass. A plasticizer was necessary, and the plasticizer used in the PVB often caused the polycarbonate to develop stress cracks and haze, and accordingly, to have low light transmission properties.
The initial problems appear to have been solved in the laminated safety glass described in U.S. Pat. No. 3,888,032, which has achieved wide commercial success. The laminate comprises polycarbonate reinforced glass wherein the polycarbonate and glass are bonded to one another by an interlayer of aliphatic polyurethane. Polyurethane provides sufficient adhesion to the glass and to the polycarbonate, and no stress cracking or cloudiness developes in the product.
Despite the commercial success of the transparent aliphatic polyurethane laminated product, there has been a continuing effort to develop less expensive products, particularly since aliphatic polyurethane is an expensive component. This invention provides new glass laminates, with and without layers of polycarbonates, and other reinforcing transparent plastics, which are considerably less expensive than the aliphatice polyurethane laminates, and which at the same time are every bit as satisfactory, if not more so, with regard to adhesion, strength and clarity. Laminates according to this invention comprise at least one layer of glass laminated directly to an ionomer resin film.
In the specification and claims the terms "ionomer" or "ionomer resin" mean an extrudable resin comprising ionically cross-linked ethylene or alpha olefin-carboxylic acid copolymers and mixtures thereof. Of interest are the ionically cross-linked copolymers prepared from a combination of ethylene, styrene or propylene monomers and acrylic acid, methacrylic acid and maleic anhydride monomers. Furthermore of particular significance are the sodium or zinc cross-linked ethylene or alpha olefin-carboxylic acid copolymers, i.e. methacrylic or acrylic acid, copolymers. Properties which distinguish ionomer resins from other polyolefin heat-seal polymers are their high clarity, melt strength, solid-state toughness and resistance to oil/fat permeation. Ionomer resins are generally commercially available as either a sodium or a zinc ionomer, and are available in a wide variety of grades. Amine salts of the copolymers are also included, as are the acid form, partially neutralized acid form, and metal salts of the acid copolymers. Although all grades of ionomer resins generally exhibit the properties noted above when compared to other thermoplastic polymers, sodium ionomers are known for exceptional toughness and resistance to fats and oils, while zinc ionomers exhibit outstanding adhesion to unprimed foil and possess excellent chemical resistance. Sodium ionomers have proved to provide the best clarity, the zinc ionomers proving to be hazy at times. The metal ion free or unneutralized version such as Nucrel.RTM. or Primcor.RTM. are generally clear but having lower strength.
Various grades of ionomer resins are available for extrusion coating and film extrusion. It is also known that ionomer resins can be laminated with other plastic resins and exhibit adhesion to other polyolefins, nylon resins and coextrudable adhesive resins often used as bonding layers in multi-ply coextruded or laminated structures. A very wide variety of ionomer resins are manufactured by E.I. DuPont de Nemours and Company under the registered trademark "SURLYN". Other ionomer resins are those manufactured by DuPont under the name NUCREL (ethylene-methacrylic acid copolymer) and PRIMACOR (ethylene-acrylic acid copolymer) manufactured by DOW Chemical Company.
Ionomer resins have been suggested for use primarily in the area of packaging, for foods, liquids and pharmaceuticals, as well as certain industrial applications including lightweight sails, bonded cable sheath, roof underlayment and flame retardant products. In most applications, ionomer resins are offered as a superior substitute for polyethylene. In none of the literature or prior art, other than our copending application Ser. No. 490,997, filed May, 8, 1983, is there any suggestion that ionomer resins should or could be used for reinforcing glass layers or for bonding layers of glass to polycarbonate or other plastic layers, in order to form a laminated safety glass. Moreover, there is no suggestion in the literature or prior art to indicate that ionomer resins could or should be substituted generally for polyurethanes or polycarbonates.
Layers of ionomer resins can be formed by casting or extrusion, the latter being preferred. When the ionomer resin layers are sufficiently thick, polycarbonate layers can be eliminated altogether while still maintaining sufficiently acceptable degrees of light transmission, impact resistance and strength.
Ionomer resins have several advantages over polyurethane. Polyurethane is more difficult to manufacture and maintain consistent high quality, and aliphatic, for example, is frequently not clear or gel-free enough for use in windshields and the like. By contrast, ionomer resin films can be easily extruded to desired thicknesses, and at about one-half the material cost of polyurethane. Ionomer resins have demonstrated better adhesion characteristics in comparison to polycarbonates, as well as better resistance to lower temperatures and solvents. In preferred embodiments, the sufrace to which the ionomer resin is adhered may be primed to improve adhesion, as is the case with polyurethane. Silane coupling agents are suitable primers. With regard to optical properties, ionomer resins demonstrate better clarity than polyurethanes. Moreover, the ionomer resins are more hydrolytically stable to water, acids and bases, and overall, are less likely to weaken with time. This greatly enhances the useful life of laminates made in accord with the present invention.